What a fricking great name... The Space Vampires! However, for a movie that wants to be taken seriously, Lifeforce is definitely the better choice.
This movie starts out a little like Alien, with a crew of space explorers coming across a strange vessel with even stranger creatures inside. When that is said, those two movies are very different, and thankfully so.
I really enjoyed myself while watching Lifeforce and for many different reasons. One being the mystery of the strange aliens, another being the setting of London... quickly becoming a true post-apocalyptic nightmare. The third being the "heroes", who are very scientific in their approach and don't go all crazy with the guns and violence. It feels very much like an adult science fiction movie, which is something I really appreciate.
Oh, and Patrick Steward is a treat to watch... even if only for a little while.